The present invention generally pertains to telephone communications and is specifically directed to improvements in cordless telephones and cordless telephone systems relating to compactness, cost and signal interference.
A typical cordless telephone system includes a cordless telephone and a base unit. The base unit is connected to the telephone lines. The base unit includes an antenna, a transmitter and a receiver for communicating an RF carrier signal that is modulated by telephone switching signals and audio signals to and from the cordless telephone. The cordless telephone includes a speaker and a microphone, and also an antenna, a transmitter and a receiver for likewise communicating telephone switching signals and audio signals to and from the base unit via an RF carrier signal. The RF carrier signal transmitted by the cordless telephone has a different center frequency f.sub.c from the RF carrier signal transmitted by the base unit.
Switching signals representative of numeric characters are generated in the cordless telephone by operating a typical telephone mechanical dialing mechanism to generate dialing pulse signals. Switching signals for initiating "off-hook" and "on-hook" switching functions are generated by removing the telephone hand set from its cradle and by replacing the same respectively. In a typical prior art cordless telephone the removal of the hand set enables the transmitter and receiver in the cordless telephone to communicate signals to the base unit.
Upon enablement of the transmitter, a control signal is generated in the cordless telephone and transmitted to the base unit. Upon receipt and detection of the control signal the base unit seizes the telephone lines so as to enable audio signals and switching signals from the cordless telephone that are received by the base unit within a given audio frequency band to be passed onto the telephone lines.
In order to prevent interference when signalling the base unit so that a transmitted control signal does not cause an unrelated base unit in the same physical area to seize the telephone lines, the control signal is encoded as a discrete control signal having a predetermined frequency in or above the given audio frequency band, and the base unit enables the telephone lines to be seized only in response to the detection of such discrete control signal.
Cordless telephones typically are battery powered and include a switch for energizing or de-energizing the telephone so that the battery can be preserved when it is not desired to use the cordless telephone. When the cordless telephone is energized, it is enabled to receive and detect a "ring" signal from the base unit and to provide the ring signal to the speaker.